The term "welding alloy" is here used to refer to a metal which is adapted to be utilized in conjunction with a welding process and is to be joined at least in part to a body of spheroidal graphite cast iron.
The welding alloy may be in the form of welding wire or rod, i.e. wire or rods which can strike an arc so that material from the wire or rod is deposited as a weldment on or adjacent the spheroidal graphite cast iron. It may be provided as a filler metal which is melted by an arc or torch, or heat generated by some other means. It may be a transition piece which is connected by welding or metallic bonding to a spheroidal graphite cast iron body.
In all cases the iron-based alloy of the invention is utilized in autogenous and electrical welding of components, at least one of which is composed of the nodular cast iron.
Connection welds of workpieces and structural elements which may include or are constituted by nodular cast iron bodies are common to join such bodies together or to weld such bodies to cast steel, forging steel or other steel-based materials.
Whenever welding is carried out for such purposes and under these conditions, a problem arises when the excess carbon from the graphite nodules is dissolved in the iron, e.g. the welding pool, and because of rapid cooling of the latter, induces the formation of cementite in the welding zone.
Cementite has a higher hardness than the surrounding area which may be detrimental for further processing and introduces a range of undesired properties into the weld region.
For one thing, such a weld can only be worked by grinding, which itself is a disadvantage, limiting utility of the process.
Another disadvantage is that the mechanical properties in the weld region are largely unpredictable or vary from place to place.
German Pat. No. 1,184,186, Swiss Pat. No. 441,953 and Austrian Pat. No. 263,479 are all directed to the development of weld materials and processes which prevent the formation of cementite in the weld region.
It has been found, however, that the use of these welding materials and techniques is only effective under a very limited set of conditions and circumstances, i.e. the techniques do not have universal applicability. As a practical matter they can only be effective when practiced by highly skilled and specially trained personnel, which is a serious drawback.
Furthermore, the connecting welds have workpieces and structural components of nodular cast iron which, in accordance with the teachings of the art, cannot be used as strengthening welds.